San Ygnacio is a census-designated place (CDP) in Zapata County, Texas, in the United States. As of the 2010 census, the CDP population was 667. It is named for the prominent Spanish saint, Ignatius of Loyola. The portion of the community between the Rio Grande and U.S. Highway 83 is listed on the National Register of Historic Places as San Ygnacio Historic District.
San Ygnacio, originally a Mexican pueblo, was founded in 1830 by settlers from nearby Guerrero, Tamaulipas on the outskirts of the recently established Uribeno Ranch. Frequent Comanche attacks in the early days of San Ygnacio necessitated the use of defensive stone architecture which has endowed the present area with uncharacteristically enduring historical sites from that period.
San Ygnacio is also historically notable for its involvement in the short-lived revolution of the Rio Grande Republic, which was established at meetings which were convened in the town in 1839.
San Ygnacio played an important role in the Garza Revolution from 1891 to 1893. Multiple small battles were fought near the town in both Mexican and American territory.
San Ygnacio was attacked in June 1916 by either Mexican Carrancistas of Seditionists.